It would be truer to the original yes, but I don't know about making "sense". Given the quick load times its quite likely that after clicking the start button, we can usually expect that they are already ready. I'm quite impatient myself, and given that I try songs many, many times, this would mean adding about an extra 2 minutes of time just spent waiting each Osu! session i play
Tens, I think you need to try playing ouendan before these comments! The countdown occurs before the first note in a length song introduction period - not before the song starts playing. I had this planned actually - was going to look at adding it last night (along with a "skip" button for when you cant be bothered listening to the intro ). Expect to see this appear in the near future!
Also, since there's a large number of beatmaps already out there, I was thinking you could probably make it at default count down on the beat (even if the song previously didn't have a countdown), and give it an option to select whether it will count down on the half or quarter as well. Just a thought.
It wouldn't be optional, and would be on the whole beat. I haven't forgotten about this, but we'll see. I get too distracted with these feature requests and things like the song selection screen and storyboarding are falling further and further into the void .